Rebreathers, Partially closed or fully closed?

[Eric__U]

dosen't the rb-80 have most of the major deep cave records?

 

[padiscubapro]

dosen't the rb-80 have most of the major deep cave records?

Some PENETRATION records are held by the RB-80 but most of the deeper stuff is all CCR.. The deepest cave dives are all done on CCRS the record dives are in the 180+ meter ( 600ft) range with runtimes in the 6 hour range..

 

[caveseeker7]

Eric, I'm not sure about any official records the RB80 holds. Doesn't really matter to me anyway. The RB80 is routinely used for extreme cave penetration, both depth and distance, by WKPP in Florida and EKPP in Europe. It was specifically designed and build for this task, so it should excell at it.

However, plenty of other rebreathers have been used as well. For years the Cis-Lunar was first choice, and it too was developed for deep caving as done by USDCDT.
Inspirations are routinely used in caves around the world and have been for several years. Prisms have been used there as well, and more recently the Megalodon has gained popularity with some CCR cavers.

MKs, Drägers and a myriad of homebuilds and conversions have succesfully found their way into and out of caves.

 

[db8us]

I agree, that the question abut record is not important. The cave dictates the profile and we have to either accept or reject the dive.
An we do not look for caves that are "short but deep" to do another record.
When we ran out of shallowe caves (less than 330ft) we will have to move to the deeper ones anyway

 

[padiscubapro]

I agree, that the question abut record is not important. The cave dictates the profile and we have to either accept or reject the dive.
An we do not look for caves that are "short but deep" to do another record.
When we ran out of shallowe caves (less than 330ft) we will have to move to the deeper ones anyway

I agree usage is going to go deeper, but on 600ft depths even relatively short ones, the required decompression of an SCR over a CCR becomes much greater and requires lots of cylinders to the point where risk is increasing as exposures increase..

I played with a few profiles (RGBM) for relatively short exposures.. for example 18 minutes to get to 180m then staying there just another 17 minutes.. On a ccr with the setpoint backed down and decompressing only at 1.2po2, the required RT is around 300 minutes, on an SCR/OC combo running an agressive profile (including dumping all he starting at 21m) with 5 deco mixes (to try and speed things along) the same dive would be in the area of 450 minutes (without oxygen breaks which add atleast another hour).. Even with an effiiency of 5 to 1 its still alot of gas and inwater time...

 

[db8us]

Breaks do not extend the total divetime !

 

[padiscubapro]

Breaks do not extend the total divetime !

It depends on how you calculate your profiles..

I know some people don't alter their profiles and count time on a low po2 mix as the same as on their oxygen others do not..

Its not uncommon for decompression software to reduce your credit during that time (if the mix is hypoxic enough no credit is given at all) so the run time IS increasing...

On very deep dives it appears the shallow stops must be extended beyond what programs like Vplanner and RGBM tell us.. I haven't played with Gap enough to see how it handles "air" breaks but Vplanner gives virtually no credit for a hypoxic switch so all your break time is added onto the original profile.

Try it for yourself, generate a profile that requires "air" breaks and try it with the function turned off and again with it turned on.. the lower the oxygen content the less credit you are given..

 

[db8us]

Yes, but the software is wrong on that.
The slwoer tissues still feed the faster compartments while on break-gas (like 17/55) and when switching back to O2 the fast tissues are almost immedialtely unloaded.
We usually do 12Min O2, 8Min on Trimix
A profile like that is described for example here:
http://www.ekpp.org/projects/gourneyras03_07/push.html

Michael

 

[padiscubapro]

Yes, but the software is wrong on that.
The slwoer tissues still feed the faster compartments while on break-gas (like 17/55) and when switching back to O2 the fast tissues are almost immedialtely unloaded.
We usually do 12Min O2, 8Min on Trimix
A profile like that is described for example here:
http://www.ekpp.org/projects/gourneyras03_07/push.html

Michael

Its just a different protocol (which very high physical fitness probably helps out).. There is no solid evidence which is right (so there is no danger in adding in some extra room for error).. What evidence does show on deeper dives the shallow stops have to be extended even over those that add in break time.. All the models seem to start breaking down at around the 100m mark, they still seem to work ok for another 50m (RGBM is supposted to be good to 180m) to varying degrees depending on initial ascent rates, slower initial ascents seem to help alot...

Cave dive profiles GENERALLY don't have rapid LARGE changes in depth and are definately not square profiles so there is definately more room for pushing the profiles towards the agressive side, the same protocols probably wount yield the same results on a square dive for the general population..

I'm also not saying a design like the RB-80 cant be used in 200m dives, its just the inwater requirements are going to be MUCH MUCH greater than someone on a CCR, and IMHO a higher risk.

 

[Mverick]

For anyone on this list that isn't familar with John I would like to point out that this guy has quite a reputation in the NY area - see copy of posting put out on the NWD site February this year.

"Any persons on the list that have been taken in by John Taylor scaming people for a rebreather please email Paul Blanchet at ussdpv@juno.com . The above said person is now at the 13th precinct in NYC. The Detectives would like to talk to you"

The rig he used to own was brought, checked out at SMI and is now used for research and tagging sharks.

If your going to do business with this guy be careful.
Shas

I'm wondering one thing. Did he have problems with the Prism unit? What shape was it in when you all got it back?